Analysis of information systems for hydropower operations

The operations of hydropower systems were analyzed with emphasis on water resource management, to determine how aerospace derived information system technologies can increase energy output. Better utilization of water resources was sought through improved reservoir inflow forecasting based on use of hydrometeorologic information systems with new or improved sensors, satellite data relay systems, and use of advanced scheduling techniques for water release. Specific mechanisms for increased energy output were determined, principally the use of more timely and accurate short term (0-7 days) inflow information to reduce spillage caused by unanticipated dynamic high inflow events. The hydrometeorologic models used in predicting inflows were examined to determine the sensitivity of inflow prediction accuracy to the many variables employed in the models, and the results used to establish information system requirements. Sensor and data handling system capabilities were reviewed and compared to the requirements, and an improved information system concept outlined

Critical Currents of Josephson-Coupled Wire Arrays

We calculate the current-voltage characteristics and critical current I_c^{array} of an array of Josephson-coupled superconducting wires. The array has two layers, each consisting of a set of parallel wires, arranged at right angles, such that an overdamped resistively-shunted junction forms wherever two wires cross. A uniform magnetic field equal to f flux quanta per plaquette is applied perpendicular to the layers. If f = p/q, where p and q are mutually prime integers, I_c^{array}(f) is found to have sharp peaks when q is a small integer. To an excellent approximation, it is found in a square array of n^2 plaquettes, that I_c^{array}(f) \propto (n/q)^{1/2} for sufficiently large n. This result is interpreted in terms of the commensurability between the array and the assumed q \times q unit cell of the ground state vortex lattice.Comment: 4 pages, 4 figure

Arp 65 interaction debris: massive HI displacement and star formation

Context: Pre-merger interactions between galaxies can induce significant changes in the morphologies and kinematics of the stellar and ISM components. Large amounts of gas and stars are often found to be disturbed or displaced as tidal debris. This debris then evolves, sometimes forming stars and occasionally tidal dwarf galaxies. Here we present results from our HI study of Arp 65, an interacting pair hosting extended HI tidal debris. Aims: In an effort to understand the evolution of tidal debris produced by interacting pairs of galaxies, including in situ star and tidal dwarf galaxy formation, we are mapping HI in a sample of interacting galaxy pairs. The Arp 65 pair is one of them. Methods: Our resolved HI 21 cm line survey is being carried out using the Giant Metrewave Radio Telescope (GMRT). We used our HI survey data as well as available SDSS optical, Spitzer infra-red and GALEX UV data to study the evolution of the tidal debris and the correlation of HI with the star-forming regions within it. Results: In Arp 65 we see a high impact pre-merger interaction involving a pair of massive galaxies (NGC 90 and NGC 93) that have a stellar mass ratio of ~ 1:3. The interaction, which probably occurred ~ 1.0 -- 2.5 $\times$ 10$^8$ yr ago, appears to have displaced a large fraction of the HI in NGC 90 (including the highest column density HI) beyond its optical disk. We also find extended ongoing star formation in the outer disk of NGC 90. In the major star-forming regions, we find the HI column densities to be ~ 4.7 $\times$ 10$^{20}$ cm$^{-2}$ or lower. But no signature of star formation was found in the highest column density HI debris, SE of NGC 90. This indicates conditions within the highest column density HI debris remain hostile to star formation and it reaffirms that high HI column densities may be a necessary but not sufficient criterion for star formation.Comment: Accepted in A&

Hot Populations in M87 Globular Clusters

We have obtained HST/STIS far- and near-UV photometry of globular clusters in four fields in the gE galaxy M87. To a limit of m(FUV) = 25 we detect a total of 66 globular clusters (GCs) in common with the deep HST optical-band study of Kundu et al. (1999). Despite strong overlap in V- and I-band properties, the M87 GCs have UV/optical properties that are distinct from clusters in the Milky Way and in M31. M87 clusters, especially metal-poor ones, produce larger hot HB populations than do Milky Way analogues. Cluster mass is probably not a factor in these distinctions. The most metal-rich M87 GCs in our sample are near Z_sun and overlap the local E galaxy sample in estimated Mg_2 line indices. Nonetheless, the clusters produce much more UV light at a given Mg_2, being up to 1 mag bluer than any gE galaxy in (FUV-V) color. The M87 GCs do not appear to represent a transition between Milky Way-type clusters and E galaxies. The differences are in the correct sense if the clusters are significantly older than the E galaxies. Comparisons with Galactic open clusters indicate that the hot stars lie on the extreme horizontal branch, rather than being blue stragglers, and that the EHB becomes well populated for ages > 5 Gyr. We find that 43 of our UV detections have no optical-band counterparts. Most appear to be UV-bright background galaxies, seen through M87. Eleven NUV variable sources detected at only one epoch in the central field are probably classical novae. [Abridged]Comment: 70 pages, 25 figures (including 4 jpgs), 7 tables. To appear in AJ. Full resolution version available at http://www.astro.virginia.edu/~rwo/m87/m87-hotpops.pd

Husimi Maps in Lattices

We build upon previous work that used coherent states as a measurement of the local phase space and extended the flux operator by adapting the Husimi projection to produce a vector field called the Husimi map. In this article, we extend its definition from continuous systems to lattices. This requires making several adjustments to incorporate effects such as group velocity and multiple bands. Several phenomena which uniquely occur in lattice systems, like group-velocity warping and internal Bragg diffraction, are explained and demonstrated using Husimi maps. We also show that scattering points between bands and valleys can be identified in the divergence of the Husimi map

The Extended Shapes of Galactic Satellites

We are exploring the extended stellar distributions of Galactic satellite galaxies and globular clusters. For seven objects studied thus far, the observed profile departs from a King function at large r, revealing a ``break population'' of stars. In our sample, the relative density of the ``break'' correlates to the inferred M/L of these objects. We discuss opposing hypotheses for this trend: (1) Higher M/L objects harbor more extended dark matter halos that support secondary, bound, stellar ``halos''. (2) The extended populations around dwarf spheroidals (and some clusters) consist of unbound, extratidal debris from their parent objects, which are undergoing various degrees of tidal disruption. In this scenario, higher M/L ratios reflect higher degrees of virial non-equilibrium in the parent objects, thus invalidating a precept underlying the use of core radial velocities to obtain masses.Comment: 8 pages, including 2 figures Yale Cosmology Workshop: The Shapes of Galaxies and Their Halo

Orientational pinning and transverse voltage: Simulations and experiments in square Josephson junction arrays

We study the dependence of the transport properties of square Josephson Junctions arrays with the direction of the applied dc current, both experimentally and numerically. We present computational simulations of current-voltage curves at finite temperatures for a single vortex in the array ($Ha^2/\Phi_0=f=1/L^2$), and experimental measurements in $100\times1000$ arrays under a low magnetic field corresponding to $f\approx0.02$. We find that the transverse voltage vanishes only in the directions of maximum symmetry of the square lattice: the [10] and [01] direction (parallel bias) and the [11] direction (diagonal bias). For orientations different than the symmetry directions, we find a finite transverse voltage which depends strongly on the angle $\phi$ of the current. We find that vortex motion is pinned in the [10] direction ($\phi=0$), meaning that the voltage response is insensitive to small changes in the orientation of the current near $\phi=0$. We call this phenomenon orientational pinning. This leads to a finite transverse critical current for a bias at $\phi=0$ and to a transverse voltage for a bias at $\phi\not=0$. On the other hand, for diagonal bias in the [11] direction the behavior is highly unstable against small variations of $\phi$, leading to a rapid change from zero transverse voltage to a large transverse voltage within a few degrees. This last behavior is in good agreement with our measurements in arrays with a quasi-diagonal current drive.Comment: 9 pages, 9 figure

The Different Structures of the Two Classes of Starless Cores

We describe a model for the thermal and dynamical equilibrium of starless cores that includes the radiative transfer of the gas and dust and simple CO chemistry. The model shows that the structure and behavior of the cores is significantly different depending on whether the central density is either above or below about 10^5 cm-3. This density is significant as the critical density for gas cooling by gas-dust collisions and also as the critical density for dynamical stability, given the typical properties of the starless cores. The starless cores thus divide into two classes that we refer to as thermally super-critical and thermally sub-critical.This two-class distinction allows an improved interpretation of the different observational data of starless cores within a single model.Comment: ApJ in pres

The magnetic field structure in CTA 102 from high-resolution mm-VLBI observations during the flaring state in 2016-2017

CONTEXT: Investigating the magnetic field structure in the innermost regions of relativistic jets is fundamental to understanding the crucial physical processes giving rise to jet formation, as well as to their extraordinary radiation output up to γ-ray energies. AIMS: We study the magnetic field structure of the quasar CTA 102 with 3 and 7 mm VLBI polarimetric observations, reaching an unprecedented resolution (∼50 μas). We also investigate the variability and physical processes occurring in the source during the observing period, which coincides with a very active state of the source over the entire electromagnetic spectrum. METHODS: We perform the Faraday rotation analysis using 3 and 7 mm data and we compare the obtained rotation measure (RM) map with the polarization evolution in 7 mm VLBA images. We study the kinematics and variability at 7 mm and infer the physical parameters associated with variability. From the analysis of γ-ray and X-ray data, we compute a minimum Doppler factor value required to explain the observed high-energy emission. RESULTS: Faraday rotation analysis shows a gradient in RM with a maximum value of ∼6 × 104⁴ rad m⁻² and intrinsic electric vector position angles (EVPAs) oriented around the centroid of the core, suggesting the presence of large-scale helical magnetic fields. Such a magnetic field structure is also visible in 7 mm images when a new superluminal component is crossing the core region. The 7 mm EVPA orientation is different when the component is exiting the core or crossing a stationary feature at ∼0.1 mas. The interaction between the superluminal component and a recollimation shock at ∼0.1 mas could have triggered the multi-wavelength flares. The variability Doppler factor associated with such an interaction is large enough to explain the high-energy emission and the remarkable optical flare occurred very close in time.Accepted manuscrip